1. Field of the Invention
This invention relates to a communication method, a transmitter, a receiver, and a cellular radio communication system, and more particularly, is applicable to a portable telephone system.
2. Description of the Related Art
In the field of radio communication, a combination of high priority data and low priority data is generally transmitted. Such a typical digital radio communication system that a combination of high priority data and low priority data is transmitted will be explained below. However, in the explanation described below, one frame of transmission data is composed of the high priority data and the low priority data, and the transmission data for one frame is transmitted by one transmission slot. Note that xe2x80x9cframexe2x80x9d means data units when processing digital data, and xe2x80x9cslotxe2x80x9d means data units when transmitting digital data.
In this radio communication system, as shown in FIG. 1, two types of information are transmitted by one frame. Accordingly, one frame is divided into high priority field and low priority field. The high priority data is stored in the high priority field and the low priority data is stored in the low priority field. In this case, not only the information bits of the data to be transmitted, but also error detection and correction bits are stored in each field. Thereby, the receiving side can detect and correct the errors of the received information bits by using the error detection and correction bits.
In addition, the error detection and correction bits having a superior ability to detect and correct errors are generally added to the high priority data, and the error detection and correction bits having a comparatively inferior ability to detect and correct errors are added to the low priority data. For this reason, the error detection and correction bits added to the high priority data tends to be longer in its size.
Here, FIG. 2 shows the construction of a transmitter for actually transmitting the frame having such structure. As shown in FIG. 2, in the transmitter 1, bit stream DH1 composed of high priority data is firstly input to a first error correction bit adding circuit 2, and bit stream DL1 composed of low priority data is input to a second error correction bit adding circuit 3.
The first error correction bit adding circuit 2 calculates the error detection and correction bits based on the input bit stream DH1 and adds this error detection and correction bits to the bit stream DH1, so as to form bit stream D1 which is stored in the high priority field. The bit stream D1 is output to a frame forming circuit 4 at a later stage. In connection, the first error correction bit adding circuit 2 calculates the error detection and correction bits having a superior ability to detect and correct errors and adds this.
While, the second error correction bit adding circuit 3 calculates the error detection and correction bits based on the input bit stream DL1 and adds this error detection and correction bits to the bit stream DL1, so as to form bit stream D2 which is stored in the low priority field. The bit stream D2 is output to a frame forming circuit 4 at a later stage. In connection, the second error correction bit adding circuit 3 calculates the error detection and correction bits having an inferior ability to detect and correct errors and adds this.
The frame forming circuit 4 adds the bit stream D2 to the end of the bit stream D1 to form transmission data stream D3 for one frame, which is output to a modulating circuit 5. The modulating circuit 5 modulates the transmission data stream D3 to form transmission symbol stream D4, which is output to a transmitting circuit 6.
The transmitting circuit 6, after performing the filtering processing on the transmission symbol stream D4, performs the digital-to-analog conversion processing on this to generate transmission signal and then performs the frequency conversion processing on the transmission signal to generate transmission signal S1. The transmitting circuit 6 transmits the transmission signal S1 via an antenna 7, so as to transmit data that the high priority data and the low priority data are combined.
On the other hand, as shown in FIG. 3, in a receiver 10, the transmission signal S1 transmitted from the transmitter 1 is received at an antenna 11, which is input to a receiving circuit 12 as reception signal S2. The receiving circuit 12, after performing the filtering processing on the reception signal S2, performs the frequency conversion processing on the reception signal S2 to take out baseband signal, and performs the analog-to-digital conversion processing on the baseband signal to take out reception symbol stream D5.
A demodulating circuit 13 performs a predetermined demodulation processing on the reception symbol stream D5 taken out by the receiving circuit 12 to restore reception data stream D6 (the reception data stream D6 is not completely equal to the transmission data stream D3, and includes data error received during transmission.), which is output to a field dividing circuit 14. The field dividing circuit 14 divides the reception data stream D6 into the bit stream D7 of the high priority field and the bit stream D8 of the low priority field, and outputs these bit streams D7 and D8 to a first error detection and correction circuit 15 and a second error detection and correction circuit 16 respectively.
The first error detection and correction circuit 15 detects data errors included in the received information bits based on the error detection and correction bits included in the bit stream D7, and corrects the data errors, so as to decode the transmitted information bits, which is output as bit stream DH2 of the high priority data. Similarly, the second error detection and correction circuit 16 detects data errors included in the received information bits based on the error detection and correction bits included in the bit stream D8, and corrects the data errors, so as to decode the transmitted information bits, which is output as bit stream DL2 of the low priority data. By this processing, the receiver 10 respectively decodes the high priority data and the low priority data from the reception signal S2.
Transmitting a combination of the high priority data and the low priority data is also performed by the cellular radio communication system such as a portable telephone system actually. This point will be concretely explained below with an example of a portable telephone system.
Generally, in a portable telephone system, the area where communication service is provided is divided into cells each having a desired size, and a base station as a fixed radio station is positioned in each cell. A portable telephone device as a mobile radio station radio-communicates with the base station within the cell where the device exists, and so-called cellular radio communication system is constructed.
In such portable telephone system, to call from a portable telephone device for example, the call processing is performed by the procedure explained below. The portable telephone device firstly transmits control data composed of preamble data and message data to a base station using control channel called random access channel (RACH). The base station constantly monitors the random access channel and detects the existence of the preamble data to detect whether there is a message from the portable telephone device or not. When the preamble data is detected, the base station judges that there is a message from the portable telephone device and detects the message data, and analyzes the contents of the message data.
As a result, if the contents of the message data is a call request, the base station decides the occupational control channel (DCCH) used to communicate with the portable telephone device, and informs this channel number to the portable telephone device using the response control channel (AGCH). After this, a predetermined control processing is executed between the portable telephone device and the base station via the informed occupational control channel, so that a call processing from the portable telephone device is realized.
Control data initially sent from the portable telephone device in the call processing is composed of preamble data and message data as described above. In this case, the preamble data represents the existence of message data. The base station side detects the existence of the preamble data firstly to detect whether there is message data or not. Accordingly, if the data is prioritized in accordance with the detection order viewing from the base station side, the preamble data has the highest priority, and the message data showing the concrete contents requested has lower priority comparing to the preamble data.
To detect the preamble data corresponding to the high priority data, in the normal portable telephone system of the frequency division multiple access (FDMA) method or the time division multiple access (TDMA) method, the preamble data is not detected by decoding, but is detected by measuring the electricity of the signal of the random access channel actually.
On the contrary to this, in the portable telephone system of the code division multiple access (CDMA) method, other signals are intermingled on the band not because of the physical division such as frequency or time but the division by the difference of spread codes. Thereby, simple measurement of signal electricity can not detect the preamble data, and resultantly the preamble data is detected by decoding. However, if the electric wave of the channel being used in other cell is received at the same level even in the portable telephone system of TDMA method, this is an example of such communication environment that the preamble data can not be detected by the simple measurement of signal electricity.
Here, the portable telephone system of the CDMA method will be concretely described below with an example of such communication environment that the preamble data can not be detected by the simple measurement of signal electricity. Note that control data is also composed of one frame in this case, and the control data is transmitted by one transmission slot.
As shown in FIG. 4, as the data structure of one frame, the preamble field is formed in the first half of the frame and the information field is in the latter half. In this case, the preamble data is stored in the preamble field, and the information bits constituting message data and the error detection and correction bits of the information bits are stored in the information field.
FIG. 5 shows the transmission/reception timing in the transmitting side and the receiving side when the control data having such data structure is transmitted/received via the random access channel. As shown in FIG. 5, in the portable telephone system, the distance between the portable telephone device being the transmitting side and the base station being the receiving side is not fixed. Further, since the portable telephone device synchronizes to meet the reception timing for receiving the signal transmitted from the base station, the portable telephone device already synchronizes with the base station in the condition that the transfer delay arises at this time.
Then, since the portable telephone device transmits the control data to the base station in this condition, transfer delay further arises when the control data is received by the base station. More specifically, at the time when the base station receives the control data from the portable telephone device, transfer delay for rounds has been already generated. In this way, in the portable telephone system, the transmission timing at the transmitting side is asynchronous with the reception timing at the receiving side due to the transfer delay of electric wave.
Accordingly, in the portable telephone system, if the portable telephone device transmits the control data at the transmission timing, the control data may not arrive at the base station at a normal reception timing. The base station of the receiving side needs to decode the received control data for one time slot at the accurate decoding timing. However, at the time when signal is received in the random access channel, the base station does not know when signal arrives, so that signal is needed to be detected not only with an accurate reception timing but also with very short time intervals, and useless decoding processing has been performed to decode the control data received actually.
Also, when the control data is received in the random access channel, the base station calculates the time lag due to the transfer delay for rounds and informs this delay time to the portable telephone device via the occupational control channel. Thereby, the portable telephone device advances the timing of transmitting the control data by the delay time, so as to synchronize the transmission and reception timing with the base station of the receiving side (hereinafter, referred to as xe2x80x9ctime alignmentxe2x80x9d). In addition, the slot of the signal which is transmitted and received between the portable telephone device and the base station in the normal random access channel is shorter than the normal slot, and this prevents the interference between slots.
Here, FIG. 6 shows the construction of a transmitter for actually transmitting such control data. As shown in FIG. 6, in the transmitter 20, bit stream DPI of preamble data is firstly input to a frame forming circuit 21, and bit stream DM1 of message data is input to an error correction bit adding circuit 22.
The error correction bit adding circuit 22 calculates error detection and correction bits based on the input bit stream DM1, and adds this to the bit stream DM1 so as to form bit stream D11 to be stored in the information field (FIG. 4), which is output to the frame forming circuit 21. The frame forming circuit 21 adds the bit stream D11 to the end of the bit stream DP1 of the preamble field as shown in FIG. 4 so as to form transmission data stream D12 for one frame, which is output to a modulating circuit 23.
The modulating circuit 23 performs a predetermined modulation processing on the transmission data stream D12 to form transmission symbol stream D13, which is output to a transmitting circuit 24. The transmitting circuit 24, after multiplying the transmission symbol stream D13 by a desired spread code and performing a filtering processing, performs the digital-to-analog conversion processing to generate transmission signal. The transmitting circuit 24 then performs the frequency conversion processing on the transmission signal to generate transmission signal S10 of a predetermined band. The transmitting circuit 24 transmits the transmission signal S10 via an antenna 25, so as to transmit the control data composed of preamble data and message data.
On the other hand, as shown in FIG. 7, in a receiver 30, the transmission signal S10 transmitted from the transmitter 20 is received at an antenna 31, which is input to a receiving circuit 32 as reception signal Sll. The receiving circuit 32, after performing the filtering processing on the reception signal S11, performs the frequency conversion processing on the reception signal S11 to take out baseband signal, and performs the analog-to-digital conversion processing on the baseband signal to take out reception symbol stream D14.
The demodulating circuit 33 performs a predetermined demodulation processing on the reception symbol stream D14 taken out by the receiving circuit 32 to restore reception data stream D15 (the reception data stream D15 is not completely equal to the transmission data stream D12, and includes data errors received during transmission.), which is output to a field dividing circuit 34.
The field dividing circuit 34 divides the reception data stream D15 into bit stream D16 of preamble field and bit stream D17 of information field, which are output to a preamble detecting circuit 35 and an error detection and correction circuit 36 respectively. In connection, the field dividing circuit 34 divides the field by the time division method. More specifically, as shown in FIG. 4, the preamble field is temporally earlier than the information field, so as to divide the field by using this timing.
The preamble detecting circuit 35 judges whether the bit stream D16 is preamble data or not, and if it is preamble data, outputs control signal S12 to the error detection and correction circuit 36. The error detection and correction circuit 36 receives the control signal S12 and starts the error detection and correction processing to detect data errors included in the information bits of the received message data based on the error detection and correction bits included in the input bit stream D17, and corrects the data errors.
As a result, if the information bits of the message data is correctly decoded, the error detection and correction circuit 36 outputs bit stream DM2 of the message data to a control circuit (not shown) for controlling communication sequence, etc. Thereby, the control circuit can find the reception of message data, and can control the communication sequence in accordance with the message data.
In connection, it has been described that the field is divided by the field dividing circuit 34. However, there is also another case where the preamble data at the head of the reception data D15 is simply detected without the field division for separating data, and after the preamble data is detected as a result, the error correction processing of next message data is performed.
In the conventional communication method, when transmitting a combination of high priority data and low priority data, respective data are processed individually. However, the processing at the same level are only performed separately, and it does not consider the priority.
Also, in the conventional communication method, when transmitting control data using the random access channel for example, preamble data is detected to confirm the existence of message data. This processing can be realized easily since the preamble data and the message data are divided in the time direction. However, in a communication of the multi-carrier method which transmits data to be transmitted at the same time using a plurality of carriers, it is impossible to perform this processing in the time direction within one modulation time since the preamble data and the message data are not divided in the time direction.
Accordingly, in the case where the control data composed of preamble data and message data is transmitted by the multi-carrier method communication, it can be generally considered that the signal components of the preamble data and the signal components of the message data are extracted by dividing them in the frequency direction at the receiving side, to decode respective data. However, this method needs a high-precision filter for dividing the signal components of the preamble data and the signal components of the message data, thereby the construction of the device at the receiving side may become complicated.
Further, since the receiving side for receiving the control data via the random access channel can not judge which timing does the control data arrives at, it is needed to judge whether the control data is received or not for each very short time. There is a problem that the amount of processing becomes vast and it takes much time to process.
In view of the foregoing, an object of this invention is to provide a communication method which can perform a processing in accordance with the priority with a simple construction even if the high priority data and the low priority data are transmitted at the same time by the multi-carrier method, and proposes a transmitter, a receiver, and a cellular radio communication system which use the communication method.
The foregoing object and other objects of the invention have been achieved by the provision of a communication method, a transmitter, a receiver, and a cellular radio communication system.
According to this invention, in a communication method for transmitting high priority data and low priority data at the same time using a plurality of sub-carriers, the transmitting side transmits transmission signal in which high priority symbols composed of information bits of the high priority data and low priority symbols composed of information bits of the low priority data are positioned alternately, and each symbol of differential symbol stream obtained by differential-modulating the high priority symbol based on the differential phase between the high priority symbol and one previous low priority symbol is assigned to the sub-carrier, so that the sub-carriers on which the high priority data are superimposed and the sub-carriers on which the low priority data are superimposed are positioned alternately. The receiving side, when the transmission signal is received at a reception timing having time lag due to transfer delay, performs a predetermined reception processing on the received reception signal to obtain reception symbol stream which is the alignment of the high priority symbols and the low priority symbols positioned alternately on the time axis, detects the phase offset component from the high priority symbols of the symbol stream whose differential phase is removed, the differential phase which is obtained by differential-demodulating the reception symbol stream, and decodes the high priority data based on the signal component of the high priority symbols, and decodes the low priority data after the phase offset component is removed from the phase component of low priority symbol of the symbol stream.
Further, according to this invention, a transmitter for transmitting high priority data and low priority data at the same time using a plurality of sub-carriers, comprises transmitting means for transmitting transmission signal in which high priority symbols composed of information bits of the high priority data and low priority symbols composed of information bits of the low priority data are positioned alternately, and each symbol of differential symbols stream obtained by differential-modulating the high priority symbols based on the differential phase between the high priority symbol and one previous low priority symbol is assigned to the sub-carrier, so that the sub-carriers on which the high priority data are superimposed and the sub-carriers on which the low priority data are superimposed are positioned alternately.
Further, according to this invention, a receiver for receiving transmission signal transmitted from a transmitter, which transmits high priority data and low priority data at the same time using a plurality of sub-carriers, at a reception timing having time lag due to transfer delay, comprises: receiving means for receiving the transmission signal in which high priority symbols composed of information bits of the high priority data and low priority symbols composed of information bits of the low priority data are positioned alternately, and each symbol of differential symbol stream obtained by differential-modulating the high priority symbols based on the differential phase between the high priority symbol and one previous low priority symbol is assigned to the sub-carrier, so that the sub-carriers on which the high priority data are superimposed and the sub-carriers on which the low priority data are superimposed are positioned alternately; signal conversion processing means for performing a predetermined conversion processing on the reception signal received by the receiving means to convert it into reception symbol stream which is the alignment of the high priority symbols and the low priority symbols positioned alternately on the time axis; differential demodulating means for differential-demodulating the reception symbol stream to form the symbol stream whose differential phase is removed; first demodulating means for detecting the phase offset component from the high priority symbols of the symbol stream, and for decoding the high priority data based on the signal component of the high priority symbols; and second demodulating means for decoding the low priority data after the phase offset component is removed from the phase component of the low priority data of the symbol stream.
Further, according to this invention, the receiver comprises: receiving means for receiving the transmission signal in which high priority symbols composed of information bits of the high priority data and low priority symbols composed of information bits of the low priority data are positioned alternately, and the high priority symbol and the low priority symbol are respectively differential-modulated based on the differential phase between the symbol itself and one previous symbol, and the sub-carriers on which the high priority symbols are superimposed and the sub-carriers on which the low priority symbols are superimposed are positioned alternately; signal conversion processing means for performing the Fourier transform on the reception signal received by the receiving means to convert the high priority symbols and the low priority symbols which are lined on the frequency axis into reception symbol stream which is lined on the time axis; first differential demodulating means for differential-demodulating the reception symbol stream to form the symbol stream whose differential phase is removed; demodulating means for decoding the high priority data based on the signal component of the high priority symbol of the symbol stream; phase offset component detecting means for detecting the phase offset component from the high priority symbols of the symbol stream; phase removing means for removing the phase offset component of the high priority symbol of the reception symbol stream, and for removing the phase offset component from the phase component that the low priority symbol of the reception symbol stream has particularly; and second differential demodulating means for forming one composite symbol by composing respective symbols in the condition that there is no phase difference between the high priority symbol of the reception symbol stream and one previous low priority symbol by the phase removing means, differential-demodulating it by using adjacent composite symbol, and demodulating the differential-demodulated composite symbol to decode the low priority data.
Furthermore, according to this invention, in a cellular radio communication system in which a base station is provided for each cell wherein a predetermined area is divided to have a desired size, and a mobile station radio-communicates with the base station within the cell where the mobile station exists, the mobile station transmits via random access channel transmission signal in which preamble symbols composed of information bits of preamble data and message symbols composed of information bits of message data are positioned alternately, and each symbol of differential symbol stream obtained by differential-modulating the preamble symbol based on the differential phase between the preamble symbol and one previous message symbol is assigned to sub-carrier, so that the sub-carriers on which the preamble symbols are superimposed and the sub-carriers on which the message symbols are superimposed are positioned alternately. The base station, when the transmission signal is received at a reception timing having time lag due to transfer delay, performs a predetermined reception processing on the received reception signal to obtain reception symbol stream which is the alignment of the preamble symbols and the message symbols positioned alternately on the time axis, detects the phase offset component from the preamble symbols of the symbol stream whose differential phase is removed, which is obtained by differential-demodulating the reception symbol stream, and decodes the preamble data based on the signal component of the preamble symbols, and decodes the message data after the phase offset component is removed from the message symbol phase component of the symbol stream.
Furthermore, according to this invention, in the cellular radio communication system, the base station transmits via an initial acquisition channel transmission signal in which message symbols composed of information bits of message data and preamble symbols composed of information bits of preamble data are positioned alternately, and each symbol of differential symbol stream obtained by differential-modulating the preamble symbol based on the differential phase between the preamble symbol and one previous message symbol is assigned to sub-carrier, so that the sub-carriers on which the preamble symbols are superimposed and the sub-carriers on which the message symbols are superimposed are positioned alternately. The mobile station, when the transmission signal is received at a reception timing having time lag due to transfer delay, performs a predetermined reception processing on the received reception signal to obtain reception symbol stream which is the alignment of the preamble symbols and the message symbols positioned alternately on the time axis, detects the phase offset component from the preamble symbols of the symbol stream whose differential phase is removed, which is obtained by differential-demodulating the reception symbol stream, and decodes the preamble data based on the signal component of the preamble symbols, and decodes the message data after the phase offset component is removed from the message symbol phase components of the symbol stream.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.